Patterned Sapphire Substrate Manufacturing Method

ABSTRACT

A patterned sapphire substrate manufacturing method uses two-section dip etching procedure to improve the lateral etching rate at each etching position, so as to produce a concave-convex pattern composed of a plurality of triangular pyramid structures protruded from a surface onto an upper surface of a sapphire substrate, such that less planar area of the sapphire substrate surface will remain, and a mixed solution of sulfuric acid and phosphoric acid is used in a first dip etching step, and pure phosphoric acid or a mixed solution of sulfuric acid and phosphoric acid is used in a second dip etching step for etching the sapphire substrate to control the inclination of each triangular pyramid structure precisely, and providing a better light extraction rate for later manufactured light emitting diodes.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method of patternizing a sapphiresubstrate surface, and more particularly to an etching method ofproducing concave-convex patterns onto a sapphire substrate surfaceeffectively up to the manufacturing quality.

(b) Description of the Related Art

In general, a light emitting diode comprises a substrate, a firstsemiconductor layer, an electrode, a light emitting layer, a secondsemiconductor layer, an ohmic contact layer, and another electrode,wherein the first semiconductor layer, light emitting layer, secondsemiconductor layer, ohmic contact layer and electrodes are installedsequentially on the substrate, and the light emitting layer is justcovered onto a portion of the first semiconductor layer, and theelectrodes are installed onto the first semiconductor layer not coveredby the light emitting layer.

Sapphire or silicon carbide (SiC) is usually used as a substrate forperforming a direct epitaxial growth of a first semiconductor layer onthe substrate. Since the epitaxial growing surface of the substrate isin a planar shape, its misalignment defect is extended to quantum wellsand the crystalline quality is affected when the epitaxy is performeddirectly on the plane. Such result only affects the yield rate of thefabricated devices, but also reduces the light emitting efficiency andthe electron mobility, and fails to produce light emitting diodes with ahigher light emitting efficiency.

Therefore, roughening an epitaxial substrate surface is considered asone of the effective ways of improving the light emitting efficiency ofthe light emitting diode, and a light emitting device having a surfacetexturing substrate as disclosed in U.S. Pat. No. 6,091,085 comprises asapphire substrate, and a rough surface composed of a plurality ofprotrusions and a plurality of recessions randomly formed on a contactsurface of the sapphire substrate with a semiconductor layer by amechanical polishing method or an ion etching method, so as to improvethe light extraction efficiency.

Although the aforementioned method can improve the light extractionefficiency by roughening the sapphire substrate surface, the sapphiresubstrate surface is damaged easily due to a composition change and alattice distortion occurred at the sapphire substrate surface and causedby ion bombardments occurred during the roughening process. Furthermore,some mask materials or reacting ions are sputtered and subsided into acertain depth from the substrate surface during the process, so that thequality of epitaxial layer formed at a later stage will be affected.Similarly, the lattice structure of the sapphire substrate surface isdamaged in the mechanical polishing process, and thus the quality ofsemiconductor layer grown at a later stage will be affected, and theinternal quantum efficiency will be lowered.

Thereafter, a dry etching method and a wet etching method for producinga concave-convex pattern on a sapphire substrate surface withoutdamaging a lattice structure of the sapphire substrate surface weredisclosed. In similar etching methods, a photosensitive material (orphotoresist) is coated onto a sapphire substrate surface first, and thena mask is placed onto the sapphire substrate, wherein the mask has apattern corresponding to the concave-convex pattern, and then anexposure procedure is carried out for performing a selective lightsensing to the light sensitive material, such that the pattern on themask is transferred onto the sapphire substrate. After the exposureprocedure is completed, a photolithography is performed, so that thephotoresist obtains a same or complementary pattern of the mask pattern,and finally an etching reaction is performed to produce an expectedpattern on the sapphire substrate surface.

Although the principle of using an etching reaction to produce anexpected concave-convex pattern on a sapphire substrate surface is wellknown, there are many parameters affecting the quality of theconcave-convex pattern finally formed onto the sapphire substratesurface, and these parameters include the photoresist material, maskpattern ratio, exposure time, selection of chemical solution for dippingthe sapphire substrate, composition proportion of chemical solution,dipping temperature, dipping time, and even frequency of dipping in thechemical solution, etc.

Therefore, we are unable to predict necessary conditions from a singleparameter condition during the process of perceiving the patternedsapphire substrate manufacturing method, but we can do the evaluationsindirectly in the complicated manufacturing process to learn thenecessary conditions. It is the best measure to explore possiblecharacteristics by continuously and gradually varying the parameterconditions of similar nature.

The inventor of the present invention based on years of experience inthe related industry to conduct extensive researches and experiments,and finally invented a patterned sapphire substrate manufacturing methodto overcome the shortcomings of the prior art.

SUMMARY OF THE INVENTION

Therefore, it is a primary objective of the present invention toovercome the aforementioned shortcoming and deficiency of the prior artby providing a patterned sapphire substrate manufacturing method forcontrolling the manufacturing quality of producing a concave-convexpattern onto a sapphire substrate surface effectively.

To achieve the aforementioned objective, the present invention uses awet etching process to effectively produce a concave-convex pattern on asapphire substrate surface during a manufacturing process. Since thetemperature of the etching process keeps decreasing, and the etchingrate tends to become slower to affect the angle, and thus a two-sectiondip etching procedure is adopted to improve the lateral etching rate ateach etching position, so as to produce a concave-convex pattern havinga plurality of triangular pyramid structures protruded from the sapphiresubstrate upper surface, such that a smaller planar area of the sapphiresubstrate surface will remain, and it helps improving the yield rate ofproducing devices on the surface of the sapphire substrate at laterprocesses.

A mixed solution of sulfuric acid and phosphoric acid is used in thefirst dip etching step, and a pure phosphoric acid or a mixed solutionof sulfuric acid and phosphoric acid is used in the second dip etchingstep for etching the sapphire substrate to control the inclination ofeach triangular pyramid structure precisely, such that the lightemitting diode manufactured at a later process can obtain a better lightextraction rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a sapphire substrate of the presentinvention;

FIG. 2 is a cross-sectional view of an etching barrier coated onto anupper surface of a sapphire substrate in accordance with the presentinvention;

FIG. 3 is a cross-sectional view of a photoresist coated onto an etchingbarrier together with a mask for performing a yellow light lithographyprocess in accordance with the present invention;

FIG. 4 is a cross-sectional view of a photoresist used for completing ayellow light lithography process in accordance with the presentinvention;

FIG. 5 is a cross-sectional view of a structure after a photoresist isremoved in accordance with the present invention;

FIG. 6 is a cross-sectional view of producing a plurality of triangularpyramid frusta on a sapphire substrate after a first etch takes place inaccordance with the present invention; and

FIG. 7 is a cross-sectional view of producing a plurality of wholetriangular pyramids on a sapphire substrate after a second etch takesplace in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technical characteristics of the present invention will becomeapparent with the detailed description of the preferred embodiments andthe illustration of the related drawings as follows.

The present invention provides an etching method with a manufacturingquality capable of enhancing the manufacturing production capability toeffectively produce a concave-convex pattern on a sapphire substratesurface and controlling the concave-convex pattern produced on thesapphire substrate surface. A chemical wet etching method is used foretching the sapphire substrate into a specific concave-convex pattern,wherein the specific concave-convex pattern is composed of a pluralityof whole triangular pyramid structures protruded from the surface, and atwo-section etching procedure is adopted, and the effect of differentchemical solutions to different etching rates of each specific crystalface of the sapphire is used for controlling the angle of the triangularpyramid structures of the patterned sapphire substrate.

With reference to FIGS. 1 to 7 for a patterned sapphire substratemanufacturing method in accordance with the present invention, thepatterned sapphire substrate manufacturing method comprises thefollowing steps:

(a) Prepare a sapphire substrate 10 as shown in FIG. 1, wherein thesapphire substrate 10 has an upper surface 11 with a crystal orientation(0001). In other words, a C-plane sapphire substrate 10 is preparedfirst.

(b) Coat an etching barrier 12 as shown in FIG. 2 onto the upper surface11 of the sapphire substrate 10, wherein the etching barrier 12 is madeof silicon oxide, and the etching barrier 12 is formed onto the uppersurface 11 of the sapphire substrate 10 by a chemical vapor deposition(CVD) process or a sputtering process in accordance with a preferredembodiment.

(c) Prepare a mask 20 as shown in FIG. 3, wherein the mask 20 has aplurality of square patterns arranged with a predetermined intervalapart from each other.

(d) Coat a layer of photoresist 13 as shown in FIG. 3 onto the etchingbarrier 12, and perform a yellow light lithography process to transfer apattern of the mask 20 onto the photoresist 13.

(e) Remove the exposed area of the etching barrier 12 which is notcovered by the photoresist 13 as shown in FIG. 4, such that the portionnot covered by the etching barrier 12 is exposed from the upper surface11 of the sapphire substrate 10 (which is also the target of the etchingprocess), wherein a buffer oxide etching solution (BOE) is used forremoving the exposed etching barrier 12 in the preferred embodiment.

(f) Remove the photoresist on the etching barrier 12 as shown in FIG. 5,wherein the photoresist is removed by dipping the photoresist into anacetone solution.

(g) Perform a first etch, wherein the first etching solution is used foretching an exposed portion of the upper surface 11 of the sapphiresubstrate 10 which is not covered by the etching barrier 12 as shown inFIG. 6, such that the plurality of triangular pyramid frustum structures111 are formed onto the upper surface 11 of the sapphire substrate 10,and the etching barrier 12 is coated onto a flat top of each triangularpyramid frustum structures 111.

(h) Perform a second etch, wherein the second etching solution is usedfor etching an exposed portion of the upper surface 11 of the sapphiresubstrate 10 which is not covered by the etching barrier 12 as shown inFIG. 7, such that the plurality of triangular pyramid frustum structuresare formed into the whole triangular pyramid structure 112, and theetching barrier 12 is removed at the same time, or the etching barrier12 is removed before the second etch as described in step (h) takesplace, such that the whole triangular pyramid structure can be formed.

In a preferred embodiment, the first etching solution used for the firstetch is a mixed solution of sulfuric acid and phosphoric acid. In themixed solution, the ratio of sulfuric acid and phosphoric acid is 3:1.In addition, the first etch is preferably conducted at a temperature of270° C. The second etching solution used for the second etch is a purephosphoric acid, and the second etch is preferably conducted at atemperature of 270° C.

In another preferred embodiment, the first etching solution used for thefirst etch is a mixed solution of sulfuric acid and phosphoric acid, andthe ratio of sulfuric acid and phosphoric acid in the mixed solution is5:1. In addition, the first etch is preferably conducted at atemperature range between 150° C. and 350° C. The second etchingsolution used for the second etch is a mixed solution of sulfuric acidand phosphoric acid, and the ratio of sulfuric acid and phosphoric acidin the mixed solution is 5:1,and the second etch is preferably conductedat a temperature range between 150° C. and 350° C.

If different parameter conditions of the aforementioned preferredembodiments are used for completing the first etch, there will be someplaces on the etching barrier 12 not etched by the first etchingsolution, such that an original C-plane sapphire substrate 10 willremain. Since the etching solution has a slower etching rate on ther-plane of the sapphire substrate 10, therefore there will be threeinclined r-planes in three different orientations remained at theperiphery of an area covered by the etching barrier 12, after thesapphire substrate (which is also an exposed portion of the uppersurface 11) not protected by the etching barrier 12 is etched.

After the etching process by the first etching solution takes place, aplurality of triangular pyramid frustum structures 111 as shown in FIG.6 will be formed on the upper surface 11 of the sapphire substrate 10,wherein the triangular pyramid frustum structures 111 have a firstcrystal face with an orientation (1012), a second crystal face with anorientation (0112) and a third crystal face with an orientation (1102),wherein the three crystal faces are the aforementioned three inclinedr-planes.

The second etching solution has a slower etching rate on the C-plane ofthe sapphire substrate 10, and thus the aforementioned triangularpyramid frustum structures 101 will be formed into the whole triangularpyramid structure 112 as shown in FIG. 7 after the etching process bythe second etching solution takes place. Here, the “whole triangularpyramid structure” is defined with respect to the triangular pyramidfrustum structure. Even there are minor flaws in the triangular pyramidstructure formed after the etching process performed by the secondetching solution, such triangular pyramid structure is still consideredas the whole triangular pyramid structure 112 defined by the presentinvention.

In the whole triangular pyramid structure formed on the upper surface ofthe sapphire substrate by the patterned sapphire substrate manufacturingmethod in accordance with the present invention, the second etchingsolution is used for the etching and formation, wherein the includedangle between the inclined surface and the horizontal surface is equalto 37 degrees. Since the lateral etching rate of the second etchingsolution is faster, the inclination of the inclined plane of thetriangular pyramid gone through etches with different time durations canbe controlled. Particularly, optoelectronic semiconductor devices suchas light emitting diodes can be manufactured by using the patternedsapphire substrate of the present invention. The patterned sapphiresubstrate can effectively reduce the density of internal defectives(such as dislocation) occurred during the epitaxial process of the lightemitting diode to enhance internal quantum efficiency and lightextraction rate of the light emitting diode.

In summation of the description above, the present invention can improvethe epitaxial quality of an optoelectronic semiconductor device toenhance the optoelectric properties of the optoelectronic semiconductordevice when the patterned sapphire substrate of the present invention isapplied for manufacturing the optoelectronic semiconductor device, andthe present invention also complies with the patent applicationrequirements, and thus the invention is duly filed for patentapplication.

While the invention has been described by device of specificembodiments, numerous modifications and variations could be made theretoby those generally skilled in the art without departing from the scopeand spirit of the invention set forth in the claims.

1. A patterned sapphire substrate manufacturing method, and the sapphiresubstrate having an upper surface with a crystal orientation (0001), andthe method comprising the steps of: (a) selectively forming an etchingbarrier onto the upper surface of the sapphire substrate, such that aportion of the upper surface is exposed; (b) using a first etchingsolution to etch the exposed portion of the upper surface of thesapphire substrate, such that a plurality of triangular pyramid frustumstructures are formed onto the upper surface of the sapphire substrate,wherein each triangular pyramid structure of the plurality of triangularpyramid frustum structures has a first crystal face with an orientation(1012), a second crystal face with an orientation (0112), and a thirdcrystal face with an orientation (1102), and the first etching solutionis a mixed solution of sulfuric acid and phosphoric acid used forperforming a first etch, and the ratio of the sulfuric acid and thephosphoric acid is 3:1; (c) using the first etching solution to etch theexposed portion on the upper surface of the sapphire substrate, suchthat the plurality of triangular pyramid frustum structures are formedinto the whole triangular pyramid structures, and the second etchingsolution is pure phosphoric acid.
 2. The patterned sapphire substratemanufacturing method of claim 1, wherein the first etch is preferablyperformed at a temperature of 270° C.
 3. The patterned sapphiresubstrate manufacturing method of claim 1, wherein the second etch ispreferably performed at a temperature of 270° C.
 4. The patternedsapphire substrate manufacturing method of claim 1, wherein the etchingbarrier is formed by silicon oxide.
 5. The patterned sapphire substratemanufacturing method of claim 1, wherein the etching barrier is formedonto the upper surface of the sapphire substrate by a chemical vapordeposition process or a sputtering process.
 6. A patterned sapphiresubstrate manufacturing method, and the sapphire substrate having anupper surface with a crystal orientation (0001), and the methodcomprising the steps of: (a) selectively forming an etching barrier ontothe upper surface of the sapphire substrate, such that a portion of theupper surface is exposed; (b) using a first etching solution to etch theexposed portion of the upper surface of the sapphire substrate, suchthat a plurality of triangular pyramid frustum structures are formedonto the upper surface of the sapphire substrate, wherein eachtriangular pyramid structure of the plurality of triangular pyramidfrustum structures has a first crystal face with an orientation (1012),a second crystal face with an orientation (0112), and a third crystalface with an orientation (1102), and the first etching solution is amixed solution of sulfuric acid and phosphoric acid used for performinga first etch, and the ratio of the sulfuric acid and the phosphoric acidis 5:1; (c) using the first etching solution to etch the exposed portionon the upper surface of the sapphire substrate, such that the pluralityof triangular pyramid frustum structures are formed into the wholetriangular pyramid structures, and the second etching solution is amixed solution of sulfuric acid and phosphoric acid, and the ratio ofthe sulfuric acid and the phosphoric acid is 5:1.
 7. The patternedsapphire substrate manufacturing method of claim 6, wherein the etchingbarrier is made of silicon oxide.
 8. The patterned sapphire substratemanufacturing method of claim 6, wherein the etching barrier is formedonto the upper surface of the sapphire substrate by a chemical vapordeposition process or a sputtering process.